One of the best ways to determine the security of your network is to employ the very techniques an attacker may use to probe all the devices on the network and their capabilities. Accordingly, this chapter covered the diagnostic use of network scanning, which can reveal hidden security flaws and holes in your setup. After describing network scanning generally, I provided details about two particular techniques. First was network mapping, in which one tries to compile a list of all the devices on a network and their IP addresses. And second was port scanning, which goes deeper by determining which ports on each network device are open. Finally, I reviewed methods for protecting your own network from these techniques.